Mining and agriculture are important sources for incorporating trace elements (TE) to the environment, through the residues generated by their extractive (low grade minerals), and purification (tailings) processes, on one hand, and by constant application of fertilizers, bio-solids and amendments, on the other, thus severely modifying the ecosystem's biogeochemical cycles.
The non-treated effluents from mining, and forestry and farming activities have high concentrations of TE, which have a negative effect, mainly on the aquatic life. Within this group of contaminants, copper (Cu), cadmium (Cd), and arsenic (As) stand out. These trace elements are frequently studied due to their abundance and toxicity. The World Health Organization (WHO) has determined that the maximum concentration of As, Cu, and Cd present in water for human consumption should not exceed 0.01, 1.5, and 0.003 mg L−1.
In general, these contaminants bioaccumulate in different tissues, such as bones, liver, kidneys, and brain, and a prolonged exposure is associated to diseases such as cancer, liver and kidney damage, and mental disorders.
There are several removal methods for these type of contaminants, including chemical precipitation, ionic interchange, surface complexing, deposition, the use of membranes, and adsorption.
In the last few years, focus has been put in the use of nanoparticles, natural or synthetic, mainly due to the easy removal of contaminants from aqueous solutions.
The imogolite is a nanotubular aluminosilicate which belongs to the family of inorganic nanotubes, that due to their unique properties in terms of chemical reactivity, mechanical resistance, optical and electrical properties, and a great surface area, have been intensely studied for the past few years. The empiric formula of the imogolite is (OH)3Al2O3SiOH, with dimensions of: 2.5 nm OD, and a variable length between 100 nm and several microns.
One of the most interesting characteristics of imogolite is its capacity of absorbing selectively and simultaneously anions and cations, as a consequence of the active sites constituting their surfaces; silanols (≡Si—OH), constituting the inner surface; and aluminols (≡Al—OH, and ≡Al2—OH), predominant in the outer surface. These groups naturally functionalize imogolite, being excellent for nanotechnologic applications. Different processes of obtainment, and structural and surface modifications, have been driven by this in order to promote their uses in manufacturing electronic and optic devices, transporting and managing drugs, removing contaminants, and storing energy.
Therefore, obtaining an iron-coated imogolite having or not magnetic properties has a high industrial potential due to the physical and chemical properties it has and which few nanoparticles are able to offer.
The present invention proposes a simple methodology for obtaining a nanohybrid formed between imogolite and Fe oxide (Ferro-imogolite)
The spatial arrangement of imogolite accounts for three types of pores—intra-unitary, inter-unitary, and inter-fibrillar, which additionally allow for a selective retention per size. Its high chemical flexibility, given by the presence of two types of active surface groups (silanols (≡Si—OH), in the inner surface; and aluminols (≡Al2-OH, and ≡Al—OH), in the outer surface), which naturally functionalize, project this nanoparticle as an excellent substrate for several environmental applications. The present application presents a method for obtaining iron-coated imogolite, with or without magnetic properties, by a process based in excess-solvent impregnation.
The present application also describes the procedure for obtaining a nanohybrid, referred to as Ferro-imogolite, with the typical characteristics of a superparamagnetic nanoparticle in the case of preparing a magnetic oxide coating, the final product maintaining in this case the main properties of imogolite and magnetite. The Ferro-imogolite thus obtained is a product that presents a different behavior in comparison to the product obtained from the physical mix of the starting materials. Differences in the electrophoretic and magnetic behavior are observed, indicating that Ferro-imogolite behaves as a single nanoparticle.